Links between surface productivity and deep ocean particle flux at the Porcupine Abyssal Plain (PAP) sustained observatory

Abstract

Abstract. In this study we present hydrography, biogeochemistry and sediment trap observations between 2003 and 2012 at Porcupine Abyssal Plain (PAP) sustained observatory in the northeast Atlantic. The time series is valuable as it allows for investigation of the link between surface productivity and deep ocean carbon flux. The region is a perennial sink for CO2, with an average uptake of around 1.5 mmol m−2 d−1. The average monthly drawdowns of inorganic carbon and nitrogen were used to quantify the net community production (NCP) and new production, respectively. Seasonal NCP and new production were found to be 4.57 ± 0.27 mol C m−2 and 0.37 ± 0.14 mol N m−2. The Redfield ratio was high (12), and the production calculated from carbon was higher than production calculated from nitrogen, which is indicative of carbon overconsumption. The export ratio and transfer efficiency were 16 and 4%, respectively, and the site thereby showed high flux attenuation. Particle tracking was used to examine the source region of material in the sediment trap, and there was large variation in source regions, both between and within years. There were higher correlations between surface productivity and export flux when using the particle-tracking approach, than by comparing with the mean productivity in a 100 km box around the PAP site. However, the differences in correlation coefficients were not significant, and a longer time series is needed to draw conclusions on applying particle tracking in sediment trap analyses.

Seasonality and spatial heterogeneity of the surface ocean carbonate system in the northwest European continental shelf

“…Overall, there was a winter peak in nutrient concentrations, then a rapid decrease in the spring and summer months. The rapid depletion in nitrate (and DIC) concentrations in spring are likely to result from their assimilation in the production of organic material by phytoplankton, during the 'spring bloom' (Frigstad et al, 2015). The dominant pattern on the shelf was for low nitrate concentrations throughout the spring to summer months, in warming water.…”

“…Variation in the C:N will also have implications for methods that calculate productivity from the depletion in DIC or nitrate (Frigstad et al, 2015 and references therein) using the 'standard' C:N Redfield ratio of 6.6:1 (Anderson and Sarmiento, 1994).…”

Fluxes of carbon and nutrients to the Iceland Sea surface layer and inferred primary productivity and stoichiometry

“…This has also been seen in other comparisons between production estimates based on in situ and remote sensing data (e.g. Richardson et al, 2005;Körtzinger et al, 2008;Frigstad et al, 2015).…”

“…We calculated long-term monthly mean profiles by averaging all data for every month, for the chosen depths (every 10 m in the upper 300 m, every 50 m between 300 and 500 m, and then every 100 m from 500 down to the bottom (1900 m)) and further interpolated to the chosen depth intervals, using piecewise cubic Hermite interpolation in Matlab ® (e.g. Fritsch and Carlson, 1980). The sampling frequency for the different months during the course of the time series sampling is shown in Table 1.…”